Syringes typically comprise a tubular body having an axial piston bore within which a piston head is moved axially by means of a plunger from a position at or adjacent the proximal end of the piston bore to a position at or adjacent the distal end of the piston bore so as to dispense the contents of the space within the body ahead of the piston via a needle located at or adjacent the distal end of the body which is inserted into or under the skin of a person. Many forms of syringe are known, but they all have these general features and the term syringe will be used hereinafter to denote a dispensing device of this type.
Once a syringe has been used to draw blood or other bodily fluid from a patient or to administer a medicament or other material to a patient, problems arise in the disposal of the used syringe. The syringe can be constructed so that it can be dis-assembled and the individual components cleaned and sterilised for subsequent re-use. However, this is time consuming and costly. It is therefore common practice to dispose of the used syringe to waste, for example into a strong plastic container which is disposed of by incineration or burial. However, in handling the used syringe there is the risk that the handler may accidentally jab himself with the exposed end of the needle prior to or during insertion into the disposal container. Furthermore, the syringe is disposed of in an operative condition so that it can be retrieved from the disposal container for unauthorised re-use, for example to inject illicit drugs or the like.
In order to reduce the risk of accidental jabbing with the used needle, it has been proposed to cut or break the needle off the syringe using a mechanical cutter, such as that described in for example U.S. Pat. Nos. 4,965,426 or 4,961,541, or using a pair of manual cutters with hardened steel blades. However, this will usually leave a sharp stump of the needle exposed which can still injure a user and machines to cut or break the needle are usually expensive and cumbersome and cannot readily be used away from sources of electric power.
It has also been proposed to supply the needle as a separate item enclosed in an axial sheath which must Be removed once the needle has been mounted on the syringe before the syringe can be used. After use the sheath is re-applied axially to the needle to render the needle safe. It has been proposed in GB 2214082 A to incorporate a circumferential rib within the foot of such a sheath which engages with a circumferential groove in the mounting of the needle on the syringe so that the sheath, when pushed fully home on the needle, engages the needle in such a manner that the needle can be separated axially from the syringe when the sheath is withdrawn axially from the syringe. However, such sheaths suffer from the disadvantage that the user must locate the needle tip axially within the narrow bore of the sheath when mounting the sheath upon the needle. There is a risk that the user will stab himself with the tip of the needle in trying to do so.
In a variation of such a sheath it has been proposed, in for example GB 2217991 A, to mount a sheath having an axial slot in the wall thereof terminally upon the syringe. The sheath is pivotally mounted so that in one position it encloses the needle. When the sheath is swung aside, the needle passes transversely through the axial slot and is exposed for use. After use, the sheath is swung back to enclose the needle. However, such sheaths are intended to protect the needle before and after use, they are not intended to remove the needle from the syringe and, due to the nature of their pivot mounting would be incapable of doing so.
Such designs do not affect the operation of the syringe and replacement of the needle can thus render such syringes reusable. It has therefore been proposed, for example in U.S. Pat. No. 4,923,443, to form the plunger with a one use construction so that the plunger can be rendered inoperative once the syringe has been used. Although the syringe is now inoperative, the problems of accidental jabbing with the needle and possible re-use of the needle remain.
In PCT Application WO89/8468 it has been proposed that the plunger should incorporate a frangible section and an axial bore so that after use the plunger can be fully withdrawn and the exposed section of the plunger then broken off at the frangible section. The plunger is thus rendered inoperative and the separated portion can be used as a sheath for the needle which is inserted axially into the axial bore in the plunger. However, such a design requires the axial insertion of the needle into the bore of the plunger with its attendant risk of the user stabbing himself.
In order to minimise the risk of stabbing, it has been proposed, for example in PCT Application WO 91/03269, to provide the needle mounting and the distal end of the plunger with co-operating means whereby the distal end of the plunger engages the needle mounting at the forward end of the plunger stroke and a spring or other means withdraws the needle axially into the hollow centre of the plunger. Such a mechanism is complex and costly to manufacture and still leaves the body of the syringe operative.
The need continues for a simple and effective means for rendering a syringe inoperative and for reducing the risk of accidental injury to the user from the needle.
I have now devised a means by which a syringe can be rendered inoperative at the same time as providing a simple means for disposing of the needle which overcomes the problem of handling and disposing of a sharp object.